1. Field of the Invention
The present invention relates to pulse generators and, more particularly, to a pulse generator that has a phase and voltage varying pulse width.
2. Description of the Related Art
A pulse generator is an electronic circuit that generates a signal which has a series of square-shaped pulses that are separated by a substantially constant lower voltage, such as ground. Each pulse has a pulse width that is defined by the time between the rising and falling edges of the pulse, and a pulse period that is defined by the time between the rising (or falling) edges of two sequential pulses.
One type of pulse generator, such as a clock circuit, produces a pulsed signal that has a substantially constant pulse width and period regardless of any external conditions. By contrast, another type of pulse generator can produce a pulsed signal with a substantially constant pulse width, but with a pulse period that varies in response to changes in an external condition.
For example, a pulse generator can generate a pulsed signal with a substantially constant pulse width by using a trigger signal to set a SR flip-flop and discharge a capacitor, and a comparator output signal to reset the SR flip-flop when the capacitor charges up to a voltage that trips the comparator.
The SR flip-flop generates a rising edge when set, and a falling edge when reset. Thus, the duration of the pulse width is defined by the time required to charge up the capacitor, which remains constant. The period, however, is defined by the trigger signal, which can vary in response to changes in the external condition.
One drawback to a pulse generator that generates a constant pulse width with an SR flip-flop, a capacitor, and a comparator is that it is difficult to generate very short pulse widths, such as pulse widths that are a few nanoseconds wide.